.

[Illustration: Fig. 25 - FINISHING SPADE.]

Fig. 25 - FINISHING SPADE.

Before the main line is cut into the open brook, this should be furnished
with a wooden trough, which will carry the water across it, so that the
ditch shall receive only the filtration from the ground. Those laterals
west of the main line, which are crossed by the brook, had better not be
opened at present,--not until the water of the spring is admitted to and
removed by the drain.

[Illustration: Fig. 26 - FINISHING SCOOP.]

Fig. 26 - FINISHING SCOOP.

The other laterals and the whole of the main line, having been cut to a
depth of 3 feet, take a finishing spade, (Fig. 25,) which is only 4 inches
wide at its point, and dig to within 2 or 3 inches of the depth marked on
the stakes, making the bottom tolerably smooth, with the aid of the
finishing scoop, (Fig. 26,) and giving it as regular an inclination as can
be obtained by the eye alone.

[Illustration: Fig. 27 - BRACING THE SIDES IN SOFT LAND.]

Fig. 27 - BRACING THE SIDES IN SOFT LAND.

If the ground is "rotten," and the banks of the ditches incline to cave
in, as is often the case in passing wet places, the earth which is thrown
out in digging must be thrown back sufficiently far from the edge to
prevent its weight from increasing the tendency; and the sides of the
ditch may be supported by bits of board braced apart as is shown in Fig.
27.

[Illustration: Fig. 28 - MEASURING STAFF.]

Fig. 28 - MEASURING STAFF.

The manner of opening the ditches, which is described above, for the main
_A_ and its laterals, will apply to the drains of the whole field and to
all similar work.

*Grading the Bottoms.*--The next step in the work is to grade the bottoms
of the ditches, so as to afford a bed for the tiles on the exact lines
which are indicated by the figures marked on the different stakes.

The manner in which this is to be done may be illustrated by describing
the work required for the line from *C10* to *C17*, (Fig. 20,) after it
has been opened, as described above, to within 2 or 3 inches of the final
depth.

A measuring rod, or square, such as is shown in Fig. 28,(18) is set at
*C10*, so that the lower side of its arm is at the mark 4.59 on the staff,
(or at a little less than 4.6 if it is divided only into feet and tenths,)
and is he